The invention relates to a contact arrangement for a preselector of a step switch.
It has long been standard practice to provide a step switch with a preselector to enlarge the effective setting range. It serves either as a coarse selector for connecting or cross connecting the step windings or as converter for controlling the step winding at the start or the end of a coarse-adjustment step. Such a known preselector normally is comprised for each phase of the three fixed preselector contacts with one of the two fixed contacts, the plus or the minus contact, being connected with the third contact, the null contact.
The Bulgarian product literature xe2x80x9cOn-load Tap changer Type RS 12xe2x80x9d and xe2x80x9cOn-load Tap Changer Type 16xe2x80x9d describe a preselect or that extends longitudinally outside the insulating cylinder of the step switch. The fixed preselector contacts are arrayed in a line, have a ball-shaped contact surface, and are switched in the above-described manner by a longitudinally shiftable switching rod with a contact bridge.
German 93 08 492 describes a preselector that is set up as a multistage coarse selector and that has a separate housing. Actuation of this preselector takes place through a rotatable switching shaft. The fixed preselector contacts here also have a ball-shaped contact surface that is switchable by means of movable contacts mounted on and pivotal with the rotatable switching shaft.
Finally German 198 36 463 proposes a preselector that is mounted as a subassembly separate from the step switch in a separate insulating housing that holds a longitudinally shiftable switching rod. The fixed preselector contacts here are circular and concentrically arrayed around the switching rod in separate planes inside the insulating housing. Mounting such circular concentrically fixed preselector contacts inside such a tubular insulating housing has shown itself to be extraordinarily difficult. It is necessary to take care that for electrical reasons the entire tubular insulating housing of the preselector be made of one piece and also have no large openings, e.g. interruptions of the insulation, while however such openings are necessary in order to get the preselector contacts inside and secure them there.
It is an object of the invention to overcome this problem and provide a contact arrangement according to the invention where the circularly shaped fixed preselector contacts can be mounted in a simple manner in a tubular insulating housing that holds the preselector.
This object is achieved with the contact according to the invention having the features of the first claim. The dependent claims relate to particularly advantageous further embodiments of the invention.
The contact arrangement according to the invention has many advantages: First the fixed preselector contacts itself forms by its shape an ideal electrode and optimally uses the available inside diameter of the insulating sleeve in which it is mounted. It is mounted from inside by being as described more closely below engaged into the interior and there mounted such that its connection means extends outward through a respective hole. The entire contact arrangement is equally usable for vertical or horizontal connections outside the insulating sleeve. Furthermore the contact arrangement according to the invention makes possible a rotationally fixed and tolerance-equalizing mounting of the preselector contacts and finally makes possible the mounting of additional shielding or shield rings for voltage protection.